<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Title</title>
  <style>
    #div1{
      width:400px;
      height:400px;
      background:white;
    }
    body{
      margin:0;
      background: black;
    }
  </style>
</head>
<body>
<div id="div1">
  <svg xmlns="http://www.w3.org/2000/svg" width="100%" height="100%">
    <rect width="50" height="200" x="100" y="100" fill="red">
      <animate attributeName="width" dur="1" from="50" to="200" fill="freeze"></animate>
    </rect>
  </svg>
</div>
</body>
</html>
